Unable to create a database diagram

Hi,
I have installed on my pc sql server 2005.I used to be able to create diagrams.Something happened to the pc so I had to uninstalled sql and installed back again.Now I started having challenge in creating diagram.It tells me that I am not allowed cos I am not the owner of the db.
AdventureWorksDW does work ie allows me to but it does not create any relationship with any of it's tables and that means I cannot create a cube using ssas.
I'll be happy to get effective replys
Ta!

Did you apply sql2k5 sp3? By the way, you should post it in sql2k5 forum.

Can you post the exact error message that it is displaying when you try and create a diagram? Is there any extra information in the error log?